The present invention relates to mobile tracking units for a vehicle tracking system and, more particularly, to mobile tracking units employing motion sensors for reducing power consumption therein under predetermined conditions.
A significant requirement for mobile tracking units used in vehicles which generally lack a power source, such as freight railcars, shipping containers and the like, is to have relatively low electrical power consumption characteristics. Mobile tracking units used in a power-starved environment must be substantially power efficient in order to provide reliable and economical operation. Typically, the mobile tracking unit includes a navigation set, such as a Global Positioning System (GPS) receiver or other suitable navigation set, responsive to navigation signals transmitted by a set of navigation stations which can be either space- or earth-based. In each case, the navigation set is capable of providing data indicative of the vehicle location based on the navigation signals. In addition, the mobile tracking unit can include a suitable electromagnetic emitter for transmitting to a remote location the vehicle position data and other data acquired with sensing elements in the vehicle. Since both the navigation set and the emitter are devices which, when energized, generally consume a large portion of the overall electrical power consumed by the mobile tracking unit, it is desirable to control the respective rates at which such devices are respectively activated so as to reduce the overall power consumption of the mobile tracking unit. For presently available mobile tracking units, use of a motion sensor, such as an accelerometer, has been suggested to detect shock or impact events which the vehicle encounters during routine use. However, no suggestion has been made of using the motion sensor for controlling the respective rates at which the aforementioned devices are activated so as to substantially reduce the overall power consumption of the mobile tracking unit.